[Elecraft] Issue 12 re Astron Power Supply

[Don Wilhelm]

Using a fused Rigrunner to connect from the K3 to a power supply can 
cause excessive voltage drop.  There are 6 points of contact.  The APP 
contact to the rigrunner itself (2 contacts, the negative must be 
considered as well).  There are 2 at the fuse contacts, and there are 2 
at the the cable connecting the output of the Rigrunner.  Add an 
additional 2 for the connection to the K3 - that makes a total of 8.
If you consider a 1mohm contact resistance (a practical estimate), then 
you have an 0.008 ohm resistance between the power supply and the K3.
  At 17 amps current draw for a K3 at 100 watts, the expected IR drop 
with that configuration is 0.136 volts due to contact resistance alone.
Add to that the resistance of the wire (#12 wire at 20 degC of 1.558 
ohms per 1000 ft.), you have an additional 3.116 milliohms resistance in 
a 5 foot cable of #12 wire - for a total of  over 1.0 volts from the #12 
wire.

In other words, the total contact resistance of the 8 powerpole 
connectors is not as great as the resistance of  5 feet of #12 wire.

Yes, connect the the K3/K3S directly to the power supply for best 
results, but if you connect through  a Rigrunner,, expect some added 
voltage drop.

The voltage drop through properly assembled APP connectors is low but 
not zero.

73,
Don W3FPR

On 4/16/2018 4:51 PM, Joe Subich, W4TV wrote:
> On 2018-04-16 4:26 PM, hawley, charles j jr wrote:
>> So 4 sets of power pole connectors plus 2 fuses.
> 
> Even if the power pole connectors are assembled perfectly and
> mated with optimum tension, the resistance in just the four
> (15 A) power pole connectors in the negative lead is equivalent
> to nearly 40 feet of #12 copper wire!
> 
>> The voltage at the rig, K3, now drops a volt when putting out 100
>> Watts.
> 
> With the equivalent of 50 feet of power cable (4 connectors plus a
> 10 foot physical cable), I would not be surprised.  Assuming 20A
> in transmit (on 15A power poles!), a 1V drop represents 0.05 Ohms
> of total circuit losses .... that's pretty good for 10 feet (x2)
> of cable plus eight connectors (4 in the + lead, 4 in the - lead)
> and the switching device (probably a Schotkey diode).  However,
> the 0.05 Ohms in the negative lead is probably ten times higher
> than in a braided bonding connection directly from the K3 chassis
> to the power supply chassis.
> 
> I'm surprised that only 75% went through the ground path - that
> indicates the ground path has 1/3 as much resistance as the "right"
> (V- lead) path.
> 
> 73,
> 
>     ... Joe, W4TV
> 
> 
> On 2018-04-16 4:26 PM, hawley, charles j jr wrote:
>> About 75% went thru the ground path. The 10 ga to the rig went from 
>> Astron to a battery switching device in case of power outage, to rig 
>> runner and to rig. So 4 sets of power pole connectors plus 2 fuses. 
>> I’m thinking of changing some of that too. The voltage at the rig, K3, 
>> now drops a volt when putting out 100 Watts.
>>
>> Chuck Jack
>> KE9UW
>>
>> Sent from my iPhone, cjack
>>
>>> On Apr 16, 2018, at 3:14 PM, Wes Stewart <wes_n7ws at triconet.org> wrote:
>>>
>>> I would hope that "much of the current..." wasn't really much.  The 
>>> direct conductor from the negative terminal of the power supply to 
>>> the radio should carry the majority of the supply current,
>>>
>>> Wes  N7WS
>>>
>>>>   On 4/15/2018 7:38 PM, hawley, charles j jr wrote:
>>>> This thread prompted me to check out my Astron vs35m. It had a small 
>>>> black wire from -V connected to the bottom of the chassis. Perhaps 
>>>> it could be called a case or cabinet...more importantly, it’s what 
>>>> the green wire from the line cord is connected to. I disconnected 
>>>> the black wire. When it was connected, much of the current that 
>>>> would have passed thru the negative power wire from the power supply 
>>>> to the rig was shunted thru the green power cord wire, the ground 
>>>> buss bar, and other ground connections.
>>>>
>>>> Chuck Jack
>>>> KE9UW
>>>>
>>>
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